This invention relates generally to a radar detecting receiver, and more particularly to such a receiver which is surprisingly accurate in detecting selected carrier wave (CW) signals of the type generally used in radar systems while rejecting other noise or spurious signals. The invention also is particularly directed to a novel alarm system for such a receiver which indicates the relative strength of a received signal and hence the relative distance of the signal source from the receiver.
The receiver of the invention is useful in detecting the presence of radar signals emitted in both the X-and K-bands. The Federal Communications Commission of the United States has established that X-band radar signals be transmitted at 10.525 GHz with a tolerance of plus or minus 0.025 GHz and that K-band radar signals be transmitted at 24.150 GHz with a tolerance of plus or minus 0.100 GHz. The prior art has proposed a number of receivers from relatively simple crystal detectors to more sophisticated superhetrodyne type receivers for the detection of radio frequency signals in this range. Heretofore, however, the relatively broad bandwidth required to insure reception of signals within the above frequency ranges has been found to adversely affect the sensitivity of the receiver.
Moreover, considerable problems with spurious signals have been encountered. Because of the relatively broad frequency band mentioned above and the need for sufficient sensitivity to detect a radar signal at some distance, such receivers have heretofore been susceptible to interference from noise signals. Such noise signals may originate in other radio or radar bands. Additionally, a considerable number of noise or spurious signals in other radar bands have been found to be generated by some relatively "noisy" radar detector units presently in use.
The user of such a radar detector may also desire information as to the relative distance of the radar source. In this regard, it is of particular interest to know whether one is approaching the radar source or receding from the radar source. Radar detectors heretofore have generally not provided a suitable indication of such information.